1. Field of the Invention
The present invention relates to a feeding device, a feeding cassette, and an image forming apparatus.
2. Description of the Related Art
Recently, an image forming apparatus such as a copier, a printer, and a facsimile machine includes a feeding device for feeding a sheet and an image forming unit for forming an image on the sheet fed from the feeding device. Such a feeding device may include a feeding cassette that is detachable from the main body of the apparatus.
FIG. 11 is a diagram illustrating a configuration of a conventional feeding cassette 150. The feeding cassette 150 includes a sheet stacking tray 153. The sheet stacking tray 153 can be raised and lowered so that sheets S stacked on the sheet stacking tray 153 are pressed onto a feeding roller. The feeding cassette 150 further includes a trailing edge regulating plate (not illustrated). The trailing edge regulating plate can slide and regulate a position of an edge (hereinafter referred to as a trailing edge) of the sheets S stacked on the sheet stacking tray 153, on an upstream side in the feeding direction thereof. Thus, the feeding cassette 150 can accommodate the sheets S of different sizes. The feeding cassette 150 further includes a pair of side regulating portions 151 and 152. The side regulating portions 151 and 152 regulate positions of the side edges of the sheets S in a direction (hereinafter referred to as a width direction) perpendicular to the feeding direction. The pair of side regulating portions 151 and 152 is coupled with each other via a rack gear and a pinion gear (not illustrated). Thus, when the user moves one side regulating portion 151, the other side regulating portion 152 moves in conjunction with the side regulating portion 151.
Even the sheets S of a standard size such as A4 or B5 vary in outer dimensions. For example, when a dimensional tolerance in the width direction of the sheet S is ±2 mm, the side regulating portions 151 and 152 need to follow the size of the sheet S in the range of ±2 mm. Thus, conventionally, one side regulating portion 152 serves as a reference surface 152a, and a sheet pressing portion 154 of the other side regulating portion 151 presses the sheet S against the reference surface 152a. A distance y between the sheets S and the side regulating portion 152 is zeroed by appropriately setting the stroke of the sheet pressing portion 154 and the spring pressure of a spring 155. Thus, the variations in the outer dimensions of the sheets S can be accommodated to maintain the print accuracy on the side of the reference surface 152a. 
When the feeding cassette 150 is installed in the main body of the apparatus, the sheets S are likely to be pushed by inertia in the direction in which the feeding cassette 150 is installed. Thus, if the installing direction of the feeding cassette 150 is the same as the width direction (the direction indicated by an arrow 150a) of the sheets S, and the side regulating portion 152 on the rear side in the installing direction serves as the reference surface 152a in the width direction, the sheets S naturally come closer to the side of the reference surface 152a during the installation of the feeding cassette 150, thereby reducing the distance y. Thus, the spring pressure of the sheet pressing portion 154 can be lower in a case where the side regulating portion 152 on the rear side is set as the reference surface side than in a case where the side regulating portion 151 on the front side is set as the reference surface side. Such a configuration can minimize the resistance applied by the sheet pressing portion 154 to the sheets S, whereby the sheets S can be stably fed.
When changing the positions of the side regulating portions 151 and 152, the side regulating portion 151 on the front side can be operated easier than the side regulating portion 152 on the rear side. Thus, in many image forming apparatuses, the side regulating portion 151 on the front side is used as an operation portion for the user.
Japanese Patent Application Laid-Open No. 2003-160239 discusses a feeding device having a configuration where, in a pair of side regulating members for regulating the edge portions of sheets stacked on a stacking tray, the one on the rear side is fixed (locked). In the feeding device discussed in Japanese Patent Application Laid-Open No. 2003-160239, the side regulating member on the rear side is fixed, and thus the side regulating member can be prevented from falling down due to the inertia produced when the feeding cassette is inserted in the main body of the apparatus. Japanese Patent Application Laid-Open No. 2003-160239 discusses a configuration where the side regulating member on the rear side is locked or unlocked by a user directly operating a lever used for locking and unlocking the member (first and second exemplary embodiments in Japanese Patent Application Laid-Open No. 2003-160239). Japanese Patent Application Laid-Open No. 2003-160239 further discusses a configuration where the user operates a knob of the side regulating member on the front side so that the side regulating member on the rear side is locked or unlocked (third and fourth exemplary embodiments in Japanese Patent Application Laid-Open No. 2003-160239).
However, the configurations discussed in Japanese Patent Application Laid-Open No. 2003-160239 needs to be further improved in the following points. First, the first and the second embodiments in Japanese Patent Application Laid-Open No. 2003-160239 need to be improved in usability because the user needs to directly operate the lever to lock or unlock the side regulating portion on the rear side. Next, the third and the fourth exemplary embodiments in Japanese Patent Application Laid-Open No. 2003-160239 require a plurality of dedicated parts for coupling the side regulating portion on the front side with the side regulating portion on the rear side. Thus, an increase in the number of parts may cause a cost increase. Furthermore, the added dedicated parts are disposed in a space below the side regulating members, whereby the size of the feeding cassette might increase in the height direction.